Optical recording media such as an optical disk have been the focus of attention as high-density and large-capacity memory devices. There are various types of memory devices, including a ROM (read only memory) which can only be read, a WORM (write once read many times memory) that allows one writing action, and an EDRAW (erasable direct read after write) as erasable and rewritable memory. The optical recording media have a wide range of applications and are utilized by consumers and industry.
In order to achieve high speed access and durability against impact of movement, an optical recording medium has preformed grooves as guide tracks and preformed pit lines on the substrate thereof. The grooves as guide tracks are provided so that a focused laser beam is guided and scanned along a track. The pit lines are created to provide positional information (address information) on the optical recording medium. The guide tracks and the pit lines are generally called pre-formatted information sections, and are created when manufacturing the substrate of an optical recording medium.
The recording density of an optical recording medium is significantly higher than that of a portable-type magnetic recording medium such as a floppy disk. Accordingly, the optical recording medium is designed to prevent, particularly, defect and errors in a header section where address information is recorded.
FIG. 5 shows a sector format, i.e., the structure of a header section of a rewritable optical disk cartridge for use in a calculator, according to IS010089 (International Standardization Organization)/IEC (International Electrotechnical Commission) and X6271 of JIS (Japanese Industrial Standard).
A sector mark (SM) section 31 is provided for a detection of the beginning of the header section. A variable frequency oscillator (VFO) section 32a, a VFO section 32b, and a VFO section 32c are synchronization patterns provided for a detection of clock pulses used for demodulating a signal. Address mark(AM) sections 33 are provided to indicate the start of address information sections (hereinafter referred to as the ID sections) 34a to 34c. The ID (identification data) sections 34a to 34c include the same address information. A post-amble (PA) section 35 is provided to absorb an overflown demodulated channel bit string from the ID sections 34a to 34c.
As described above, in an optical disk cartridge, the same address information is recorded three times in the ID 34a to 34c and the address information is read out using a majority logic so as to prevent an erroneous detection of address information due to defect and errors in the header section.
Actually, an optical disk is sectored so that one complete rotation of the optical disk forms one track. Each track is divided into 17 sectors, and a header section shown in FIG. 5 is provided at the beginning of each sector. The optical disk having such a structure is reliable in practical use and allows the reproduction of address information.
On the contrary, with an optical disk having a conventional structure, since the header section occupies a large space of memory, a user area of the memory which is available for a user is decreased.
For example, in a 5-inch optical disk having 1024 bytes/sectors, there are 18750 tracks in total in one side of the optical disk, and each header section occupies 52 bytes. Therefore, the volume of data for the header sections becomes 52.times.17.times.18750=16,575 MB. This volume is equivalent to 5% of the total memory capacity of the optical disk, i.e., 1024.times.17.times.18750=326.4 MB.
Although an optical disk has a large capacity, an increased user area is demanded at present as the necessity of image data processing is increased. In order to consider the spread of multimedia in future, it is necessary to increase the user area of an optical disk even by a small amount. However, at present, as described above, since a large number of bytes are allocated for the header sections to improve the reliability of the optical disk, the capacity of the user area becomes smaller.